K. G. Arun
Articles written in Journal of Astrophysics and Astronomy
Volume 37 Issue 4 December 2016 Article ID 0030 Review
Poonam Chandra G. C. Anupama K. G. Arun Shabnam Iyyani Kuntal Misra D. Narasimha Alak Ray L. Resmi Subhashis Roy Firoza Sutaria
With the high sensitivity and wide-field coverage of the Square Kilometre Array (SKA), large samples of explosive transients are expected to be discovered. Radio wavelengths, especially in commensal survey mode, are particularly well-suited for uncovering the complex transient phenomena. This is because observations at radio wavelengths may suffer less obscuration than in other bands (e.g. optical/IR or X-rays) due to dust absorption. At the same time, multiwaveband information often provides critical source classification rapidly than possible with only radio band data. Therefore, multiwaveband observational efforts with wide fields of view will be the key to progress of transients astronomy from the middle 2020s offering unprecedented deep images and high spatial and spectral resolutions. Radio observations of Gamma Ray Bursts (GRBs) with SKA will uncover not only much fainter bursts and verifying claims of sensitivity-limited population versus intrinsically dim GRBs, they will also unravel the enigmatic population of orphan afterglows. The supernova rate problem caused by dust extinction in optical bands is expected to be lifted in the SKA era. In addition, the debate of single degenerate scenario versus double degenerate scenario will be put to rest for the progenitors of thermonuclear supernovae, since highly sensitive measurements will lead to very accurate mass loss estimation in these supernovae. One also expects to detect gravitationally lensed supernovae in far away Universe in the SKA bands. Radio counterparts of the gravitational waves are likely to become a reality once SKA comes online. In addition, SKA is likely to discover various new kinds of transients.
Volume 43 All articles Published: 5 July 2022 Article ID 0039 TRANSIENTS
GRB 210217A: a short or a long GRB?
DIMPLE DIMPLE KUNTAL MISRA ANKUR GHOSH K. G. ARUN RAHUL GUPTA AMIT KUMAR L. RESMI S. B. PANDEY LALLAN YADAV
Gamma-ray bursts are traditionally classified as short and long bursts based on their $T_{90}$ value (the time interval during which an instrument observes 5% to 95% of gamma-ray/hard X-ray fluence). However, $T_{90}$ is dependent on the detector sensitivity and the energy range in which the instrument operates. As a result, different instruments provide different values of $T_{90}$ for a burst. GRB 210217A is detected with different duration by
Volume 43 All articles Published: 13 September 2022 Article ID 0066 TRANSIENTS
Modeling the late-time merger ejecta emission in short gamma ray bursts
ANKUR GHOSH KUNTAL MISRA S. V. CHERUKURI L. RESMI K. G. ARUN AMITESH OMAR DIMPLE N. K. CHAKRADHARI
The short gamma ray bursts (GRBs) are the aftermath of the merger of binary compact objects (neutron star–neutron star or neutron star–black hole systems). With the simultaneous detection of gravitational wave (GW) signal from GW 170817 and GRB 170817A, the much-hypothesized connection between GWs and short GRBs has been proved beyond doubt. The resultant product of the merger could be amillisecond magnetar or a black hole depending on the binary masses and their equation of state. In the case of a magnetar central engine, fraction of the rotational energy deposited to the emerging ejecta produces latetime synchrotron radio emission from the interaction with the ambient medium. In this paper, we present ananalysis of a sample of short GRBs located at a redshift of $z\leq 0.16$, which were observed at the late-time to search for the emission from merger ejecta. Our sample consists of seven short GRBs, which have radio upper limits available from very large array and Australian telescope compact array observations. We generate the model light curves using the standard magnetar model incorporating the relativistic correction. Using the model light curves and upper limits we constrain the number density of the ambient medium to be 10$^{-1}$–10$^{-3}$ cm$^{-3}$ for rotational energy of the magnetar $E_{\rm rot}\sim 5\times 10^{51}$ erg. Variation in ejecta mass does not play a significant role in constraining the number density.
Volume 44, 2023
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